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VetInfo Digest October 2004

General Information about Poisonings and Pets

Specific Poisons:

Ethylene Glycol

Permethrin

Rodenticides

Batteries

Lilies

Lead

NSAIDS

ASPCA National Animal Poison Control Center

This Month's Note:

If your dog was given a ProHeart 6 ™ injection for heartworm prevention this year it is pretty likely that you know by now that it has been recalled by the FDA. Adverse reactions to the injection were reported at a high enough rate that the FDA felt that a recall of the medication was the only responsible step. It is not clear at this time if all, or even most, of the reactions reported were actually due to the drug. It is important to keep this in mind if your dog is one of the ones who received this heartworm prevention injection. As long as the injection did not occur within the last month or so it is unlikely that a reaction will occur and it is not necessary to be overly concerned that your pet will have any effect from this injection. It is still important to consider the possibility if an unexplained illness occurs, but this is just a precautionary step that should always be taken when a pet has an unexplained illness while a medication is being used.

Remember that it is not necessary to switch immediately to a different heartworm prevention medication. There is no indication that ProHeart 6 didn't work to prevent heartworms. A switch to one of the monthly heartworm tablets should be made 6 months after the date of the last ProHeart 6 injection.

Poisonings and Pets

It is not unusual at our practice for a pet owner to bring in an obviously ill pet with the predetermined notion that it has been deliberately poisoned by a neighbor. In almost all of these types of cases it turns out the pet is ill for some other reason. Accidental poisonings, on the other hand, are not highly unusual in veterinary medicine. This month I am going to try to cover the poisonings we see most commonly in our practice and to also cover some of the nonpoisonous substances that have an unjustified bad reputation as a possible poison. There are a number of terms that are used when discussing toxicology and it is important to know at least a few of them:

A poison is a substance that has the potential to harm an animal by interfering with the normal processes for maintaining life.

A toxin is a poison that is produced by a biologic process. The distinction between a poison and a toxin is subtle and the term toxin is often used as a substitute name for any type of poison. Technically, though, a chemical or compound that does not come from a plant or animal is not a toxin. Recently, to make matters even more confusing it has become common in the literature for toxins to be referred to as biotoxins. This term would be redundant except for the tendency to use the words poison and toxin interchangeably. Toxicity is a measurement of the ability of a poison to cause an adverse effect or the dosage of the poison necessary to cause adverse effects.

Toxicosis is a disease state that has been induced by a poison. It is important to note that it is entirely possible to have a toxicosis that will not result in death. Any adverse effect on an animal is regarded as a toxicosis. This can be a real sticking point when trying to evaluate information about poisonous substances. Most people assume that when there is a report of a poisoning there was at least some risk of death to the pet during the poisoning episode. This is not necessarily true, though. A substance that causes vomiting but no more serious symptom than that will still be considered to be a poison by a toxicologist.

The lethal dose of a poison is the dose that causes death. Most of the time this is broken down further and reported as the dosage that causes death in some percentage of patients. The LD50 would be the dose of a poison which would kill 50% of the animals exposed to it. An LD10 would the dose that kills 10% of the animals exposed to it. Sometimes this is also called the lethal concentration, usually for poisons that are meant to mixed with water or with foods prior to use.

There are two terms used to describe the levels at which poisons cause an observed adverse effect. They are the NOAEL or "no observed adverse effect level" and the LOAEL, or "lowest observed adverse effect level". The difference between these might be easiest to envision by thinking about walking towards the edge of a cliff. If it takes 20 steps to get right the cliff edge then the NOAEL is 20 steps. The 21st step would the LOAEL in this example. That would be the point that you stepped off the cliff.

While the LD50, NOAEL and LOAEL are useful in assessing the possible risk to a pet from exposure to a known poison it is important to remember that individual pets vary widely in their susceptibility to the effects of a poison . For this reason it is not uncommon for veterinarians to react cautiously when poisonings are possible and to advise treatment even when the risk of death is not especially high.

It is really very important to understand the difference between the lowest observed adverse effect level and the lethal dose when discussing poisons. Frequently veterinarians advise treatment for toxicoses when it seems likely that the toxin has exceeded the LOAEL even when the risk of death is extremely low. This can cause confusion about the seriousness of a toxicosis and lead to undue worry after exposure to poisons that are quite capable of causing adverse effects but are very unlikely to actually cause death.

It is possible for a substance to be both a medication and a poison or toxin. In fact, most medications are poisonous if enough of the medication is administered. This might not a common problem if humans were not a great deal larger than many of their pets. When a 5 lb. poodle ingests thirty 5mg enalapril tablets it is more likely he or she will have an adverse effect than the owner would if a similar number of pills were ingested by the owner.

Medications that are safe to use for humans may not be safe for dogs or cats. Medications that are safe to use in dogs may not be safe to use in cats. It is critically important to understand that different species of animals have different reactions to many substances and that a substance may be a poison in one species and non-harmful or even beneficial in another species. Lots of people kill their pets every year by making the mistake of using their own medications or over the counter medications to treat suspected illnesses.

There are a number of poisons whose ability to cause harm depends on how the pet is exposed to the medication. Some poisons must be inhaled to cause toxicosis while others have to be ingested or applied to the skin in order to cause harm. Whenever it is possible to tell, it is important to let your veterinarian know the possible route of exposure when a poisoning is suspected.

An antidote is a substance that counteracts the effect of a specific toxin or poison. There are specific antidotes for a number of toxicoses. If a specific antidote is not available there are also substances that help a great deal in the treatment of pets who have been poisoned in more general ways. The best example of one of these latter substances is activated charcoal, which is given orally and absorbs many toxins or poisons, safely transporting them out of the digestive tract. It is more likely that an emergency clinic (EVC) will have some of the specific antidotes than a general veterinary practice so in a true emergency it is best to go to the EVC directly than to try to get in contact with your vet in many instances.

General information on exposure to poisons

When a poisoning is suspected the best possible situation is to know what poison a pet was exposed to, the amount that it ingested (or was exposed to by other means), the time the exposure occurred and when symptoms on poisoning started, if they have started already. There is no substitute for keeping your wits about you when dealing with a suspected poisoning and gathering up the container the poison came in, if available, looking around just enough to make a good guess as to how much of the poison the pet was exposed to or getting the phone number of anyone who might have inadvertently poisoned a pet, such as an exterminator, who may be able to provide additional information on the substance the pet was exposed to.

The labels of many substances that can be poisonous have warnings or information to use in case of accidentally exposure to the chemical. Read the label. If it says to induce vomiting there are several ways to do this at home. Syrup of ipecac can be given to pets to induce vomiting. The dosage for dogs is 1 to 2 ml per kilogram of body weight or about 0.5 to 1ml per pound of body weight. This also works out to 1 teaspoonful per 5 to 10 lbs. of body weight. The dosage for cats is 3.3 ml/kg or about 1 teaspoonful per 4 pounds of body weight. Administering hydrogen peroxide will cause most pets to vomit if enough of it is given. The recommended dosage for dogs is 1 to 2 ml/kg or 0.5 to 1ml/lb. It is usually necessary to repeat the dosage once or twice to get vomiting to occur. The same dosage of hydrogen peroxide works for cats but the dosage should only be repeated once in this species.

If it is not possible to identify a specific poison your vet may only be able to treat the symptoms of the poisoning and hope for the best. In some cases the signs of a toxicosis are distinct enough to allow identification of the poison without prior knowledge of what it was but don't count on this. In situations in which it really seems likely that a poisoning has occurred but it is unclear what the poison it is still possible to treat symptomatically successfully in many cases.

One situation that often catches people unprepared is the sudden death of a pet. Often in this circumstance there is some worry over the possibility of poisoning. My best advice in this circumstance is to ask for a post mortem exam (necropsy exam) in order to determine a cause of death, if possible. It is best to be prepared to make this decision in advance because many people have a very hard time with the emotional aspects of having a necropsy exam done while also dealing with the sudden loss of a valued friend. Over the long term, though, many people have expressed regret over not pursuing an accurate diagnosis at the time of death. It just helps to know what happened. This is particularly important when there is more than one pet in a household and there is any chance of exposure to a poison that might affect more than one pet.

It is important when discussing necropsy examination as a diagnostic tool to point out that most general practice veterinarians are not going to be able to determine whether a specific poison was responsible for the death of a pet. In most cases this doesn't cause problems because in most cases in which poisoning is suspected another cause of death can be identified on necropsy examination. If it is certain, or near certain, that a poison caused a pet's death and it is important to know exactly which poison was involved it is best to ask that the pet's necropsy examination be performed by a board certified veterinary pathologist. It is almost always possible to find veterinary pathologists at veterinary schools but there are also a number of veterinary pathologists who work for commercial laboratories that provide necropsy examination services. If it is necessary to test serum or tissues for poisons the cost can be quite high so it is important to get some idea of the cost in advance when making arrangements for testing. If the cost is prohibitive you can always elect to have just the post mortem examination done and hope that a cause for death is found.

Knowing where your local emergency clinic is, or being aware of the emergency options available to you if an emergency clinic is not within a reasonable driving distance before an emergency occurs is extremely important. Time can be the most critical factor in the success of treatment for several poisonings and is important in almost all poisonings. If activated charcoal can be given within an hour of the ingestion of a poison it can absorb it is nearly twice as effective if given within the first hour as it is when started more than an hour after the ingestion of a poison. Several types of poisoning can only be successfully treated if treatment starts within a specific time period. Make sure that you know where to go after your vet's regular hours or on weekends or holidays.

Antifreeze Poisoning

In our practice the two most common poisonings in dogs are ethylene glycol (antifreeze mostly) poisoning and ingestion of rodenticides (mouse or rat poisons). While ethylene glycol poisoning is not as common in cats, it does occur. The toxic effects of ethylene glycol are fairly well known and this has been one of the few things used for deliberate poisonings which have been treated at our practice.

Ethylene glycol poisoning requires treatment within 2 to 4 hours for maximum benefits and treatment more than 8 hours after ingestion may not be sufficient to prevent death. In most cases of successful treatment for this poisoning the pet is either seen ingesting the ethylene glycol or exposure is a known possibility. Early symptoms of ethylene glycol poisoning include a sudden increase in drinking and urinating, intoxication that resembles alcohol intoxication, salivation, vomiting and sometimes sneezing or coughing if the poison is inhaled rather than ingested. Later signs of ethylene glycol poisoning are signs related to kidney failure, including an inability to produce urine, vomiting, extreme depression, rapid respiratory rates and seizures.

It takes approximately 4.4 ml of ethylene glycol per kilogram of body weight to cause death in dogs and approximately 1 to 1.5ml per kilogram of body weight to cause death in cats. This means that a teaspoonful of undiluted ethylene glycol can cause death in cats and that several tablespoonfuls can kill a small dog.

It is possible to test for ethylene glycol poisoning. An in-house test kit, the EGT (tm) by PRN Pharmacal, is available for use in veterinary hospitals. This test utilizes a blood sample to determine if ethylene glycol is present. It takes about a half hour to run and ties up the time of one technician so it is sometimes necessary to draw blood, start treatment and then to go back and do the test, depending on how recent the exposure to ethylene glycol might have been. In this case it is usually a good idea to get a enough blood to send out a test to a commercial lab to confirm questionable results from the in-house test kit. The relative infrequency of ethylene glycol poisoning and limited life of the test kit make it hard for rural and small clinics to keep this test kit available but emergency clinics often have it.

Treatment for ethylene glycol poisoning involves attempting to absorb as much of the toxins from the intestines as possible using activated charcoal given as soon as possible, intravenous fluid therapy and the use of the antidote 4-methylpyrazole (4-MP). If 4-MP is not available ethanol, usually in the form of grain alcohol, can be given intravenously. This produces an extreme "drunken" state pretty quickly and has a higher risk than the use of 4-MP, however. In a few areas of the country hemodialysis (kidney dialysis) is available for dogs and this is considered to be standard treatment in humans.

The key thing to remember about ethylene glycol poisoning is that it is necessary to treat pets who have been exposed to this poison as quickly as possible. You must go to an emergency veterinary clinic or find another veterinarian if there is going to be a delay in seeing your own vet. Early appropriate treatment is the only chance for a good outcome when ethylene glycol poisoning has occurred.

Permethrin

In cats, the most common poisoning that we see in our practice at this time is permethrin poisoning. This occurs when clients use "spot on" flea control products containing permethrin and labeled for use in dogs on their cat. This must be a fairly easy mistake to make because we see two or three cats a year with permethrin toxicosis. This causes severe tremoring, salivation and seizures in cats. It is unclear what percentage of cats who are treated with permethrin based flea products die from the exposure but some do. Most cats will respond to treatment with muscle relaxants such as methocarbamol and diazepam (Valium Rx). There is no specific antidote for permethrin poisoning. Thoroughly washing the permethrin off the hair and skin if it is accidentally applied can prevent poisoning and doing this helps even after clinical symptoms of permethrin poisoning have occurred.

Once in a while small dogs develop muscular weakness after permethrin products are applied but this is a transient effect and dogs are generally not considered to be as susceptible to permethrin toxicosis as cats are. The best way to avoid this poisoning is to read the label of all flea control products before applying them to any pet, but especially before applying them to a cat.

Rodenticides

There are two major classes of rodenticides that are still used commonly in the United States and a third class that was used in the U.S. recently enough that exposure is still possible and this poison may still be used in other parts of the world.

Anticoagulant containing rodenticides are the most common types. Warfarin, the first of the anticoagulants, has been replaced in many rodent poisons with second generation relatives, especially bromadialone, brodifacoum and difethialone. The second generation anticoagulants work at lower dosages and have a longer duration of action, up to a month in some cases. As the name implies, these rat and mouse poisons work by interfering with blood clotting, causing the rat or mouse to bleed to death. If pets ingest adequate quantities of these toxins the same effect occurs in pets.

In many instances of exposure to rat and mouse poisons our clients have been aware of the fact that the pet ingested the poison. In these cases it is often possible to limit the damage done by making the pet vomit if the ingestion occurred within four hours and by administration of activated charcoal as soon as vomiting stops, if a high dosage of the rodenticide was ingested or if there was more than a four hour delay in therapy. Vitamin K administration will keep the anticoagulant action of the warfarin based rodenticides from working, making it a true antidote for the poison. It must be given for at least 14 days when warfarin is ingested, 21 days when bromadialone is ingested and for 30 days for all other second generation anticoagulants. It is best to test for blood clotting ability using a prothrombin time test 48 hours after the last dose of Vitamin K, just to be sure there is no residual effect of the poison.

Bromethalin is a rodenticide that is not warfarin based. If your pet is exposed to this poison and you have the label or can identify the poison it is critically important that you make sure your vet hears the word bromethalin and doesn't confuse it with broudifacoum or bromadialone. These are very different poisonings. Bromethalin usually comes as a tan or green pellet. It causes brain swelling and increased fluid pressure in the brain which leads to tremors, seizures, excitability and death. Dogs may die with doses as low as 2.5mg/kg of body weight and cats are even more susceptible with death occurring in some cats with doses as low as 0.45mg/kg.

If the poisoning is discovered within a couple of hours of the event it is best to cause vomiting. It is important to use activated charcoal and a cathartic (or a combined product like Toxiban tm) and to repeat the administration for as long as three days, repeating the dosing every 4 to 8 hours. If seizures occur it is necessary to use seizure controlling medications. While it seems logical to treat the brain swelling with drugs that might reduce this there doesn't seem to be much evidence that works. It can take a very long time for a pet to recover from bromethalin poisoning, sometimes as long as 2 weeks or more.

Cholecalciferol is an active form of Vitamin D3 that has been used as a rodenticide. We used to see poisonings from this product pretty frequently but we have not had a poisoning from it for several years. My impression was that it had been removed from the market but I am not able to confirm that so I have to assume that I have been wrong in this assumption. I am not sure why we have not seen poisonings from cholecalciferol lately. The predominant brand name we dealt with for this product was Rampage (tm).

Ingestion of cholecalciferol causes severe rises in calcium level very rapidly. This leads to vomiting, diarrhea, increased drinking and urinating (marked increases) and rapid onset of kidney failure. Unfortunately there are several other causes of rises in calcium levels, including cancers, hyperparathyroidism, chronic kidney failure and idiopathic (unexplainable) calcium rises that sometimes occur in cats. Rapid testing for these conditions is usually not possible, with the exception of kidney failure, so it may be necessary to treat first and try to diagnose the actual cause of increased calcium levels later if there is any suspicion of exposure to cholecalciferol.

If you read vitamin labels carefully you will note that some multi-vitamin products contain cholecalciferol. The levels in vitamin products are so low that it would be very difficult for a toxicosis to occur from ingestion of vitamins.

If it is clear that exposure to cholecalciferol has occurred it is best to induce vomiting. Repeated doses of activated charcoal should be given. Intravenous administration of saline containing fluids helps to reduce calcium levels in the blood stream. The diuretic furosemide is useful in eliminating calcium from the blood stream and prednisone is also useful for this purpose. It may take several weeks of treatment before calcium levels stay within normal limits.

I can't really leave the topic of rodenticides without telling one story. Very early in my veterinary career a man brought a dog in for examination for the sole reason that it did not greet him at the mailbox when he came home from work. He was convinced this was a sign of severe illness. There were no physical signs of illness at all and routine lab work, which the owner insisted on, was normal. Based solely on the owner's extreme concern this dog was kept for observation. The next morning it started to have obvious clinical signs of hemorrhaging. We were able to start treatment immediately and the dog lived. This experience taught me three very important things. The first was that some owners have such deep bonds with their pets that they can tell something is wrong before it is obvious to me. The second was that one of the first signs of rodenticide poisoning is depression or pain that makes pets unwilling to move around. Now whenever we see sudden unexplained depression or pain we keep rodenticide poisoning high on our list of differentials. The third thing I learned is that a concerned pet owner can and should insist on lab work, referral to a specialist, additional examination procedures or whatever it takes to convince themselves that there isn't a problem -- even when the vet isn't sure those procedures are necessary. Being your pet's advocate can sometimes be the difference between life and death.

Batteries

I don't really know why pets swallow batteries. I suspect that cats, who tend to swallow things like watch or hearing aid batteries, are probably just playing with them. I think that some dogs really think that the battery is meant to be swallowed.

While some people worry about lead poisoning when their pet has swallowed a battery the real problem is actually the potential for burns from the caustic substances in the battery. If the pet is salivating, has dark gray to black coloring on its teeth or seems to be in discomfort then it is most likely that the battery was chewed on and broken open. In this case, it is best to X-ray the pet to confirm that the battery was swallowed and to remove it surgically. It can be tempting to try to retrieve batteries with an endoscope but due to the potential for burns of the esophagus as it is removed this is usually not a good idea.

If there are no clinical signs but an X-ray confirms that a battery has been swallowed, it is harder to figure out what to do. If the battery is in the esophagus it should be removed. This is most common in cats who have ingested small batteries. In this case, it is best to remove the battery with an endoscope, if possible because it is the quickest method and because surgical approaches to the esophagus are difficult and do not heal well. If the battery is in the stomach and looks undamaged on the X-rays and appears as if it is small enough for the pet to pass through the digestive system, it is OK to let that happen. It is important to check the stools daily until the battery is identified. If it hasn't been passed within 2 to 3 days then X-rays should be taken again and if necessary, surgery done to remove the battery.

So far, in our practice, if the battery was chewed the pet has not swallowed it and if it was swallowed it will pass through, with the possible exception of 9 volt batteries. We haven't seen a pet that tried to swallow a C or D cell battery. We have had one pet who tried to swallow a 9-volt battery unsuccessfully when its owner tried to take it from him -- and I think some dogs probably could swallow one of these batteries.

If there are oral burns it is best to wash the oral cavity repeatedly with water to dilute the battery acids. Sucralfate seems to help in protecting oral and esophageal tissues from developing deeper burns or damage.

Lilies

Easter is a dangerous time for cats, because Easter lilies are very toxic to cats. Other lily species, including day lilies, are also toxic but exposure to them seems less common. Why cats are so susceptible to poisoning by lily species has not been fully documented but eating these plants causes severe kidney failure. Most cats will also have gastrointestinal irritation that causes vomiting. This is rapidly acting toxin and it is necessary to act quickly if your cat is observed eating lilies or if vomiting or signs of GI distress occur and ingestion of lilies is a possibility.

If a cat has not vomited on its own after eating lilies it is best to induce vomiting and then to try to absorb as much of the lily toxin as possible using activated charcoal. The most important part of treatment for lily poisoning is intravenous fluid therapy to help the kidneys continue to function enough to eliminate the toxin. The only alternatives if kidney function does stop is hemodialysis or peritoneal dialysis, which must be kept up until kidney function returns. There are some reported cases in which this has happened. If you have cats it is best not to have any lily species in your house or garden.

Lead poisoning

Lead poisoning is not a huge problem in pets but every now and then it is seen. This used to occur fairly commonly in rural areas when pets ingested animals that had been shot with lead shot but this does not seem to be as big a problem now as it has been in the past. Many pets have been exposed to lead as the result of eating paint chips. Just as in people, there can be acute lead poisoning in which the exposure happens quickly and causes serious disease quickly or chronic lead poisoning resulting from long term exposure to increased levels of lead in the environment. Our practice area is surrounded by water so the most common cause of lead poisoning in our area is ingestion of fishing sinkers, generally because they are in close proximity to bait. Lots of other things contain lead, though. A partial list includes linoleum, lead paints, old toys, lead based art paints and older forms of caulking. If you live in an older home it is hard to be certain that lead is not present in some form or another.

Exposure to high levels of lead cause an acute illness with symptoms that include seizures, incoordination, blindness and depression. Chronic exposure to lower levels of lead may cause vomiting, diarrhea, loss of appetite, depression, behavioral changes and low grade anemia. These signs are so nonspecific that the only way to diagnose them is to have a high degree of suspicion and to test blood lead levels.

Treatment of lead poisoning involves removing lead from the digestive tract, treating the symptoms present (such as seizures) and the use of chelating drugs that complex with lead and help to remove it from the body. These medications include calcium EDTA, penicillamine and succimer. Treatment must be continued until lead levels are within normal ranges. The prognosis for successful treatment of chronic lead poisoning is usually pretty good. If a lead source can be identified and removed this is also true for acute lead poisoning.

Non-steroidal Anti-inflammatory Medications (NSAIDS)

Non-steroidal anti-inflammatory medications are commonly used in veterinary medicine for pain relief. These are valuable medications and contribute a great deal to the quality of life for many pets. However, these medications are also among the most likely to cause adverse reactions, ranging from gastrointestinal irritation to liver or kidney damage. While I do not want to discourage the use of these medications, nor to consider them as poisons, I feel that it is important to cover one aspect of their use. If you are giving your pet any NSAID and your pet stops eating or shows a definite drop in appetite, stop the medication and call your veterinarian as soon as possible to report the change in appetite. This is often the first sign of an adverse reaction when using these medications. This class of medications includes aspirin, carprofen (Rimadyl Rx), deracoxib (Deramaxx Rx), meloxicam (Metacam Rx)and tepoxalin (Zubrin Rx). Ibuprofen is also a non-steroidal anti-inflammatory medication and is frequently involved in toxicoses in dogs and cats. Do not give your pet ibuprofen! Stopping the administration of the NSAID may resolve the problem but specific treatment for ulcers, kidney damage or liver damage may be necessary if one of these problems has occurred.

ASPCA National Animal Poison Control Center

In this issue of the VetInfo Digest I tried to cover the poisonings that we see most commonly. I did not cover acetaminophen poisoning in cats because it seems like most of our clients have figured out that any product containing acetaminophen should never be given to a cat. There are a large number of possible poisonings, including overdosages or inappropriate dosing of many medications. If you ever have any doubt about whether your pet might have been poisoned, especially if you have access to the label for the product that might be poisonous, you can call the National Animal Poison Control Center for assistance in dealing with the poisoning. The phone number is 888-426-4435. The URL for the website, which lists current fees for this service is http://www.aspca.org/site/PageServer?pagename=apcc. If you suspect an adverse reaction to a medication or product sold through your veterinarian and you can reach your veterinarian immediately, you may wish to call there first, as many of the veterinary pharmaceutical companies will pay the consultations fees of the poison control center if one of their products is suspected of being involved in a poisoning. Your veterinarian can help to make this happen by contacting the company's technical support personnel and reporting the problem to them.

Thanks for Your Support!

The VetInfo Digest is published by:

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P.O. Box 476

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The opinions expressed in this newsletter are those of Michael Richards, DVM., author.